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Substantially improve code generation for address exposed locals (aka fixed

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sized allocas in the entry block).  Instead of generating code like this:

entry:
  reg1024 = ESP+1234
... (much later)
  *reg1024 = 17


Generate code that looks like this:
entry:
  (no code generated)
... (much later)
  t = ESP+1234
  *t = 17

The advantage being that we DRAMATICALLY reduce the register pressure for these
silly temporaries (they were all being spilled to the stack, resulting in very
silly code).  This is actually a manual implementation of rematerialization :)

I have a patch to fold the alloca address computation into loads & stores, which
will make this much better still, but just getting this right took way too much time
and I'm sleepy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13554 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-05-13 07:40:27 +00:00
parent 0428962064
commit cb2fd557ee
2 changed files with 202 additions and 128 deletions
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165
lib/Target/X86/InstSelectSimple.cpp
View File

@ -86,6 +86,10 @@ namespace {
// MBBMap - Mapping between LLVM BB -> Machine BB
std::map<const BasicBlock*, MachineBasicBlock*> MBBMap;
// AllocaMap - Mapping from fixed sized alloca instructions to the
// FrameIndex for the alloca.
std::map<AllocaInst*, unsigned> AllocaMap;
ISel(TargetMachine &tm) : TM(tm), F(0), BB(0) {}
/// runOnFunction - Top level implementation of instruction selection for
@ -122,6 +126,7 @@ namespace {
RegMap.clear();
MBBMap.clear();
AllocaMap.clear();
F = 0;
// We always build a machine code representation for the function
return true;
@ -350,9 +355,7 @@ namespace {
return F->getSSARegMap()->createVirtualRegister(RC);
}
/// getReg - This method turns an LLVM value into a register number. This
/// is guaranteed to produce the same register number for a particular value
/// every time it is queried.
/// getReg - This method turns an LLVM value into a register number.
///
unsigned getReg(Value &V) { return getReg(&V); } // Allow references
unsigned getReg(Value *V) {
@ -361,36 +364,86 @@ namespace {
return getReg(V, BB, It);
}
unsigned getReg(Value *V, MachineBasicBlock *MBB,
MachineBasicBlock::iterator IPt) {
// If this operand is a constant, emit the code to copy the constant into
// the register here...
//
if (Constant *C = dyn_cast<Constant>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
copyConstantToRegister(MBB, IPt, C, Reg);
return Reg;
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
// Move the address of the global into the register
BuildMI(*MBB, IPt, X86::MOV32ri, 1, Reg).addGlobalAddress(GV);
return Reg;
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
// Do not emit noop casts at all.
if (getClassB(CI->getType()) == getClassB(CI->getOperand(0)->getType()))
return getReg(CI->getOperand(0), MBB, IPt);
}
MachineBasicBlock::iterator IPt);
unsigned &Reg = RegMap[V];
if (Reg == 0) {
Reg = makeAnotherReg(V->getType());
RegMap[V] = Reg;
}
return Reg;
}
/// getFixedSizedAllocaFI - Return the frame index for a fixed sized alloca
/// that is to be statically allocated with the initial stack frame
/// adjustment.
unsigned getFixedSizedAllocaFI(AllocaInst *AI);
};
}
/// dyn_castFixedAlloca - If the specified value is a fixed size alloca
/// instruction in the entry block, return it. Otherwise, return a null
/// pointer.
static AllocaInst *dyn_castFixedAlloca(Value *V) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
BasicBlock *BB = AI->getParent();
if (isa<ConstantUInt>(AI->getArraySize()) && BB ==&BB->getParent()->front())
return AI;
}
return 0;
}
/// getReg - This method turns an LLVM value into a register number.
///
unsigned ISel::getReg(Value *V, MachineBasicBlock *MBB,
MachineBasicBlock::iterator IPt) {
// If this operand is a constant, emit the code to copy the constant into
// the register here...
//
if (Constant *C = dyn_cast<Constant>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
copyConstantToRegister(MBB, IPt, C, Reg);
return Reg;
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
// Move the address of the global into the register
BuildMI(*MBB, IPt, X86::MOV32ri, 1, Reg).addGlobalAddress(GV);
return Reg;
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
// Do not emit noop casts at all.
if (getClassB(CI->getType()) == getClassB(CI->getOperand(0)->getType()))
return getReg(CI->getOperand(0), MBB, IPt);
} else if (AllocaInst *AI = dyn_castFixedAlloca(V)) {
// If the alloca address couldn't be folded into the instruction addressing,
// emit an explicit LEA as appropriate.
unsigned Reg = makeAnotherReg(V->getType());
unsigned FI = getFixedSizedAllocaFI(AI);
addFrameReference(BuildMI(*MBB, IPt, X86::LEA32r, 4, Reg), FI);
return Reg;
}
unsigned &Reg = RegMap[V];
if (Reg == 0) {
Reg = makeAnotherReg(V->getType());
RegMap[V] = Reg;
}
return Reg;
}
/// getFixedSizedAllocaFI - Return the frame index for a fixed sized alloca
/// that is to be statically allocated with the initial stack frame
/// adjustment.
unsigned ISel::getFixedSizedAllocaFI(AllocaInst *AI) {
// Already computed this?
std::map<AllocaInst*, unsigned>::iterator I = AllocaMap.lower_bound(AI);
if (I != AllocaMap.end() && I->first == AI) return I->second;
const Type *Ty = AI->getAllocatedType();
ConstantUInt *CUI = cast<ConstantUInt>(AI->getArraySize());
unsigned TySize = TM.getTargetData().getTypeSize(Ty);
TySize *= CUI->getValue(); // Get total allocated size...
unsigned Alignment = TM.getTargetData().getTypeAlignment(Ty);
// Create a new stack object using the frame manager...
int FrameIdx = F->getFrameInfo()->CreateStackObject(TySize, Alignment);
AllocaMap.insert(I, std::make_pair(AI, FrameIdx));
return FrameIdx;
}
/// copyConstantToRegister - Output the instructions required to put the
/// specified constant into the specified register.
///
@ -630,27 +683,24 @@ void ISel::SelectPHINodes() {
// If this is a constant or GlobalValue, we may have to insert code
// into the basic block to compute it into a virtual register.
if (isa<Constant>(Val) || isa<GlobalValue>(Val)) {
if (isa<ConstantExpr>(Val)) {
// Because we don't want to clobber any values which might be in
// physical registers with the computation of this constant (which
// might be arbitrarily complex if it is a constant expression),
// just insert the computation at the top of the basic block.
MachineBasicBlock::iterator PI = PredMBB->begin();
// Skip over any PHI nodes though!
while (PI != PredMBB->end() && PI->getOpcode() == X86::PHI)
++PI;
ValReg = getReg(Val, PredMBB, PI);
} else {
// Simple constants get emitted at the end of the basic block,
// before any terminator instructions. We "know" that the code to
// move a constant into a register will never clobber any flags.
ValReg = getReg(Val, PredMBB, PredMBB->getFirstTerminator());
}
if ((isa<Constant>(Val) && !isa<ConstantExpr>(Val)) ||
isa<GlobalValue>(Val)) {
// Simple constants get emitted at the end of the basic block,
// before any terminator instructions. We "know" that the code to
// move a constant into a register will never clobber any flags.
ValReg = getReg(Val, PredMBB, PredMBB->getFirstTerminator());
} else {
ValReg = getReg(Val);
// Because we don't want to clobber any values which might be in
// physical registers with the computation of this constant (which
// might be arbitrarily complex if it is a constant expression),
// just insert the computation at the top of the basic block.
MachineBasicBlock::iterator PI = PredMBB->begin();
// Skip over any PHI nodes though!
while (PI != PredMBB->end() && PI->getOpcode() == X86::PHI)
++PI;
ValReg = getReg(Val, PredMBB, PI);
}
// Remember that we inserted a value for this PHI for this predecessor
@ -3582,25 +3632,12 @@ void ISel::emitGEPOperation(MachineBasicBlock *MBB,
/// frame manager, otherwise do it the hard way.
///
void ISel::visitAllocaInst(AllocaInst &I) {
if (dyn_castFixedAlloca(&I)) return;
// Find the data size of the alloca inst's getAllocatedType.
const Type *Ty = I.getAllocatedType();
unsigned TySize = TM.getTargetData().getTypeSize(Ty);
// If this is a fixed size alloca in the entry block for the function,
// statically stack allocate the space.
//
if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(I.getArraySize())) {
if (I.getParent() == I.getParent()->getParent()->begin()) {
TySize *= CUI->getValue(); // Get total allocated size...
unsigned Alignment = TM.getTargetData().getTypeAlignment(Ty);
// Create a new stack object using the frame manager...
int FrameIdx = F->getFrameInfo()->CreateStackObject(TySize, Alignment);
addFrameReference(BuildMI(BB, X86::LEA32r, 5, getReg(I)), FrameIdx);
return;
}
}
// Create a register to hold the temporary result of multiplying the type size
// constant by the variable amount.
unsigned TotalSizeReg = makeAnotherReg(Type::UIntTy);

165
lib/Target/X86/X86ISelSimple.cpp
View File

@ -86,6 +86,10 @@ namespace {
// MBBMap - Mapping between LLVM BB -> Machine BB
std::map<const BasicBlock*, MachineBasicBlock*> MBBMap;
// AllocaMap - Mapping from fixed sized alloca instructions to the
// FrameIndex for the alloca.
std::map<AllocaInst*, unsigned> AllocaMap;
ISel(TargetMachine &tm) : TM(tm), F(0), BB(0) {}
/// runOnFunction - Top level implementation of instruction selection for
@ -122,6 +126,7 @@ namespace {
RegMap.clear();
MBBMap.clear();
AllocaMap.clear();
F = 0;
// We always build a machine code representation for the function
return true;
@ -350,9 +355,7 @@ namespace {
return F->getSSARegMap()->createVirtualRegister(RC);
}
/// getReg - This method turns an LLVM value into a register number. This
/// is guaranteed to produce the same register number for a particular value
/// every time it is queried.
/// getReg - This method turns an LLVM value into a register number.
///
unsigned getReg(Value &V) { return getReg(&V); } // Allow references
unsigned getReg(Value *V) {
@ -361,36 +364,86 @@ namespace {
return getReg(V, BB, It);
}
unsigned getReg(Value *V, MachineBasicBlock *MBB,
MachineBasicBlock::iterator IPt) {
// If this operand is a constant, emit the code to copy the constant into
// the register here...
//
if (Constant *C = dyn_cast<Constant>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
copyConstantToRegister(MBB, IPt, C, Reg);
return Reg;
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
// Move the address of the global into the register
BuildMI(*MBB, IPt, X86::MOV32ri, 1, Reg).addGlobalAddress(GV);
return Reg;
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
// Do not emit noop casts at all.
if (getClassB(CI->getType()) == getClassB(CI->getOperand(0)->getType()))
return getReg(CI->getOperand(0), MBB, IPt);
}
MachineBasicBlock::iterator IPt);
unsigned &Reg = RegMap[V];
if (Reg == 0) {
Reg = makeAnotherReg(V->getType());
RegMap[V] = Reg;
}
return Reg;
}
/// getFixedSizedAllocaFI - Return the frame index for a fixed sized alloca
/// that is to be statically allocated with the initial stack frame
/// adjustment.
unsigned getFixedSizedAllocaFI(AllocaInst *AI);
};
}
/// dyn_castFixedAlloca - If the specified value is a fixed size alloca
/// instruction in the entry block, return it. Otherwise, return a null
/// pointer.
static AllocaInst *dyn_castFixedAlloca(Value *V) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
BasicBlock *BB = AI->getParent();
if (isa<ConstantUInt>(AI->getArraySize()) && BB ==&BB->getParent()->front())
return AI;
}
return 0;
}
/// getReg - This method turns an LLVM value into a register number.
///
unsigned ISel::getReg(Value *V, MachineBasicBlock *MBB,
MachineBasicBlock::iterator IPt) {
// If this operand is a constant, emit the code to copy the constant into
// the register here...
//
if (Constant *C = dyn_cast<Constant>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
copyConstantToRegister(MBB, IPt, C, Reg);
return Reg;
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
unsigned Reg = makeAnotherReg(V->getType());
// Move the address of the global into the register
BuildMI(*MBB, IPt, X86::MOV32ri, 1, Reg).addGlobalAddress(GV);
return Reg;
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
// Do not emit noop casts at all.
if (getClassB(CI->getType()) == getClassB(CI->getOperand(0)->getType()))
return getReg(CI->getOperand(0), MBB, IPt);
} else if (AllocaInst *AI = dyn_castFixedAlloca(V)) {
// If the alloca address couldn't be folded into the instruction addressing,
// emit an explicit LEA as appropriate.
unsigned Reg = makeAnotherReg(V->getType());
unsigned FI = getFixedSizedAllocaFI(AI);
addFrameReference(BuildMI(*MBB, IPt, X86::LEA32r, 4, Reg), FI);
return Reg;
}
unsigned &Reg = RegMap[V];
if (Reg == 0) {
Reg = makeAnotherReg(V->getType());
RegMap[V] = Reg;
}
return Reg;
}
/// getFixedSizedAllocaFI - Return the frame index for a fixed sized alloca
/// that is to be statically allocated with the initial stack frame
/// adjustment.
unsigned ISel::getFixedSizedAllocaFI(AllocaInst *AI) {
// Already computed this?
std::map<AllocaInst*, unsigned>::iterator I = AllocaMap.lower_bound(AI);
if (I != AllocaMap.end() && I->first == AI) return I->second;
const Type *Ty = AI->getAllocatedType();
ConstantUInt *CUI = cast<ConstantUInt>(AI->getArraySize());
unsigned TySize = TM.getTargetData().getTypeSize(Ty);
TySize *= CUI->getValue(); // Get total allocated size...
unsigned Alignment = TM.getTargetData().getTypeAlignment(Ty);
// Create a new stack object using the frame manager...
int FrameIdx = F->getFrameInfo()->CreateStackObject(TySize, Alignment);
AllocaMap.insert(I, std::make_pair(AI, FrameIdx));
return FrameIdx;
}
/// copyConstantToRegister - Output the instructions required to put the
/// specified constant into the specified register.
///
@ -630,27 +683,24 @@ void ISel::SelectPHINodes() {
// If this is a constant or GlobalValue, we may have to insert code
// into the basic block to compute it into a virtual register.
if (isa<Constant>(Val) || isa<GlobalValue>(Val)) {
if (isa<ConstantExpr>(Val)) {
// Because we don't want to clobber any values which might be in
// physical registers with the computation of this constant (which
// might be arbitrarily complex if it is a constant expression),
// just insert the computation at the top of the basic block.
MachineBasicBlock::iterator PI = PredMBB->begin();
// Skip over any PHI nodes though!
while (PI != PredMBB->end() && PI->getOpcode() == X86::PHI)
++PI;
ValReg = getReg(Val, PredMBB, PI);
} else {
// Simple constants get emitted at the end of the basic block,
// before any terminator instructions. We "know" that the code to
// move a constant into a register will never clobber any flags.
ValReg = getReg(Val, PredMBB, PredMBB->getFirstTerminator());
}
if ((isa<Constant>(Val) && !isa<ConstantExpr>(Val)) ||
isa<GlobalValue>(Val)) {
// Simple constants get emitted at the end of the basic block,
// before any terminator instructions. We "know" that the code to
// move a constant into a register will never clobber any flags.
ValReg = getReg(Val, PredMBB, PredMBB->getFirstTerminator());
} else {
ValReg = getReg(Val);
// Because we don't want to clobber any values which might be in
// physical registers with the computation of this constant (which
// might be arbitrarily complex if it is a constant expression),
// just insert the computation at the top of the basic block.
MachineBasicBlock::iterator PI = PredMBB->begin();
// Skip over any PHI nodes though!
while (PI != PredMBB->end() && PI->getOpcode() == X86::PHI)
++PI;
ValReg = getReg(Val, PredMBB, PI);
}
// Remember that we inserted a value for this PHI for this predecessor
@ -3582,25 +3632,12 @@ void ISel::emitGEPOperation(MachineBasicBlock *MBB,
/// frame manager, otherwise do it the hard way.
///
void ISel::visitAllocaInst(AllocaInst &I) {
if (dyn_castFixedAlloca(&I)) return;
// Find the data size of the alloca inst's getAllocatedType.
const Type *Ty = I.getAllocatedType();
unsigned TySize = TM.getTargetData().getTypeSize(Ty);
// If this is a fixed size alloca in the entry block for the function,
// statically stack allocate the space.
//
if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(I.getArraySize())) {
if (I.getParent() == I.getParent()->getParent()->begin()) {
TySize *= CUI->getValue(); // Get total allocated size...
unsigned Alignment = TM.getTargetData().getTypeAlignment(Ty);
// Create a new stack object using the frame manager...
int FrameIdx = F->getFrameInfo()->CreateStackObject(TySize, Alignment);
addFrameReference(BuildMI(BB, X86::LEA32r, 5, getReg(I)), FrameIdx);
return;
}
}
// Create a register to hold the temporary result of multiplying the type size
// constant by the variable amount.
unsigned TotalSizeReg = makeAnotherReg(Type::UIntTy);